1. Field of the Invention
The present invention relates to a semiconductor package, and more particularly to a semiconductor package including a window lid in which an optical functional element functioning by light irradiation is mounted on an insulating substrate.
2. Description of Related Art
A semiconductor package which mounts an optical functional element functioning by light irradiation and includes a window lid (a lid body with a window) with which an element mounting surface is covered has received attention recently. One example of this kind of semiconductor package is a DMD (Digital Micromirror Device). Briefly as herein described, the DMD is an MEMS device in which multiple minute mirror surfaces (the so-called micromirror with a size of about 10 μm) are arranged as an optical control element surface. When the optical control element surface is irradiated with light corresponding to an image from a light source (lamp) for video projection through an opening for light transmission, its light is reflected by the optical control element surface and the reflected light can be reproduced on a projection screen as an image. By using the DMD, for example, there can be provided a rear projection television or a data projector of which size is small and is light weight are small while which has high brightness and high resolution.
However, it is necessary to improve heat characteristics in the periphery of the package as improvement in high brightness or other performance advances in these image reproducing apparatus. This is because there are problems that a large amount of heat is generated at the time of using such a semiconductor packages. One problem is heat discharged from an optical control element (DMD chip), and another problem is heat derived from an increase in temperature of the window lid itself (particularly, a glass window) which covers the chip mounting surface of a substrate.
The problem of heat discharged from the DMD chip can be solved by disposing a columnar thermal via inside the substrate as described in, for example, Japanese Patent Unexamined Publication JP-A-06-13491. FIG. 1 shows one example of a heat dissipation method proposed in JP-A-06-13491, and an embedded integrated circuit apparatus illustrated is constructed of a multilayer wiring substrate 101 and a thin film multilayer wiring layer 102 formed integrally with the substrate 101 thereon. Also, an electronic component (for example, an LSI element) 103 is mounted on the thin film multilayer wiring layer 102 through a die pad and an element mounting surface is covered with a metal cap 105. Also, an input-output lead 106 is connected to the multilayer wiring substrate 101. Further, a thermal via (a columnar member constructed of a material with high thermal conductivity (for example, copper)) 104 extends through multilayer wiring substrate 101 in the thickness direction, and heat from the electronic component 103 can be discharged from a heat dissipation fin 107 through this thermal via 104.
The heat derived from an increase in temperature of the window lid itself becomes a problem. In a semiconductor package such as the DMD involving light irradiation at the operation time, measures against the heat discharged from the chip can be taken by the method described in JP-A-06-13491, however it is in the present situation in which an increase in temperature of the window lid itself is not considered although the increase is not negligible. In the future, when the amount of heat of the light with which an optical functional element is irradiated from a light source increases due to high brightness, there is fear of damage or a decrease in performance of the optical functional element due to the increase in temperature of the window lid and it is necessary to take new measures against heat dissipation.